1. Field of the Invention
The present invention relates to an apparatus for measuring the content of intramuscular fat in carcasses or parts thereof.
2. Description of the Prior Art
It is well known in the art that the content of intramuscular fat (fat marbling) in beef affects the taste and consistency of the meat. Muscles with a certain degree of fat in the muscles feels tender and juicy, whereas muscles without any fat give a tough and dry feeling. In order to be able to guarantee the tenderness and taste of the meat it is therefore important to be able to determine the content of intramuscular fat of muscles in carcasses or parts thereof.
It has recently been described that the fat content of beef muscles can be predicted by measuring the muscles' impedance (see article by W. D. Slanger and M. J. Marchello in J. Anim. Sci. 72 (1994), pp. 3124-3130: "Bioelectrical Impedance Can Predict Skeletal Muscle and Fat-free Skeletal Muscle of Beef Cow Primal Cuts"). The measurement is carried out by insertion of four electrodes into a muscle. Two of the electrodes are connected to an AC generator with a frequency of 50 kHz. The two other electrodes are placed between the first electrodes so that the four electrodes are aligned. The inner electrodes are connected to a circuit measuring the voltage over the electrodes and the phase in relation to the signal of the generator. On the basis of this measurement, the meat impedance can be determined (the impedance comprises a real component, which is pure ohmic resistance, and an imaginary component, which corresponds to the phase shift). The impedance correlates to the muscle's fat content and it is thus an expression of the amount of intramuscular fat in the muscle.
The reason why four electrodes are used for the measuring is that the contact resistance between electrodes and meat is very high and may vary considerably depending on the pH and liquid content of the meat. When a constant alternating current is passed through the outer electrodes, measurements can be taken over the inner electrodes by means of a phase and amplitude detector having very high input impedance. This has the effect that the fall in voltage in the transition between the inner electrodes and the meat becomes relatively small as no current is drawn in the measuring. Variations in the contact resistance are therefore insignificant.
The above-mentioned test equipment is unsuitable for on-line measuring of intramuscular fat in abattoirs or meat processing plants. It is for instance not sufficiently reliable to comply with the requirements imposed on such equipment to allow it to be used in abattoirs to determine fat marbling.
The purpose of the invention is therefore to provide an apparatus suitable for measuring intramuscular fat under the operational conditions of abattoirs or meat processing plants. Preferably the apparatus should also be able to determine the fat content of minced meat.